Inhibition of PDE5A1 guanosine cyclic monophosphate (cGMP) hydrolysing activity by sildenafil analogues that inhibit cellular cGMP efflux.

Objectives: To determine the ability of 11 sildenafil analogues to discriminate between cyclic nucleotide phosphodiesterases (cnPDEs) and to characterise their inhibitory potencies (K values) of PDE5A1-dependent guanosine cyclic monophosphate (cGMP) hydrolysis.

Methods: Sildenafil analogues were identified by virtual ligand screening (VLS) and screened for their ability to inhibit adenosine cyclic monophosphate (cAMP) hydrolysis by PDE1A1, PDE1B1, PDE2A1, PDE3A, PDE10A1 and PDE10A2, and cGMP hydrolysis by PDE5A, PDE6C, PDE9A2 for a low (1 nm) and high concentration (10 μm). Complete IC plots for all analogues were performed for PDE5A-dependent cGMP hydrolysis.

Modulation of high affinity ATP-dependent cyclic nucleotide transporters by specific and non-specific cyclic nucleotide phosphodiesterase inhibitors.

Intracellular cyclic nucleotides are eliminated by phosphodiesterases (PDEs) and by ATP Binding cassette transporters such as ABCC4 and ABCC5. PDE5 and ABCC5 have similar affinity for cGMP whereas ABCC5 has much higher affinity for cGMP compared with cAMP. Since the substrate (cGMP) is identical for these two eliminatory processes it is conceivable that various PDE inhibitors also modulate ABCC5-transport.

Novel cGMP efflux inhibitors identified by virtual ligand screening (VLS) and confirmed by experimental studies.

Elevated intracellular levels of cyclic guanosine monophosphate (cGMP) may induce apoptosis, and at least some cancer cells seem to escape this effect by increased efflux of cGMP, as clinical studies have shown that extracellular cGMP levels are elevated in various types of cancer. The human ATP binding cassette (ABC) transporter ABCC5 transports cGMP out of cells, and inhibition of ABCC5 may have cytotoxic effects. Sildenafil inhibits cGMP efflux by binding to ABCC5, and in order to search for potential novel ABCC5 inhibitors, we have identified sildenafil derivates using structural and computational guidance and tested them for the cGMP efflux effect.

[New techniques for optimization of thiopurine therapy in leukemia and transplantation].

Background: The majority of chemotherapeutic agents are administered at fixed doses that are close to those maximally tolerated.

Material And Methods: This review is based on current knowledge about the metabolism of thiopurines and the clinical implications of genetic polymorphism in thiopurine-S-methyltransferase (TPMT).

Results: Intracellularly thiopurines, e.